In computer programming, scope is an enclosing context where values and expressions are

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<p>In computer programming, scope is an enclosing context where values and expressions are associated. Various programming languages have various types of scopes. The type of scope determines what kind of entities it can contain and how it affects them -- or semantics.</p>

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associated. Various programming languages have various types of scopes. The type of scope

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determines what kind of entities it can contain and how it affects them -- or semantics.

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Scopes can:

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* contain declarations or definitions of identifiers;

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<p>Scopes can:</p>

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* contain statements and/or expressions which define an executable algorithm or part

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thereof;

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* nest or be nested.

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A namespace is a scope that uses the enclosing nature of the scope to group logically

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* contain declarations or definitions of identifiers;

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related identifiers under a single identifier. Thus, scopes can affect the name resolution

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* contain statements and/or expressions which define an executable algorithm or part thereof;

<p>A namespace is a scope that uses the enclosing nature of the scope to group logically related identifiers under a single identifier. Thus, scopes can affect the name resolution for their contents.</p>

...a namespace is an abstract container providing context for the items (names, or

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<p>...a namespace is an abstract container providing context for the items (names, or technical terms, or words) it holds and allowing disambiguation of items having the same name (residing in different namespaces)...</p>

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technical terms, or words) it holds and allowing disambiguation of items having the

A namespace is an abstract container or environment created to hold a logical grouping

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<p>A namespace is an abstract container or environment created to hold a logical grouping of unique identifiers (i.e., names). An identifier defined in a namespace is associated with that namespace. The same identifier can be independently defined in multiple namespaces. That is, the meaning associated with an identifier defined in one namespace may or may not have the same meaning as the same identifier defined in another namespace. Languages that support namespaces specify the rules that determine which namespace an identifier (i.e., not its definition) belongs.</p>

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of unique identifiers (i.e., names). An identifier defined in a namespace is associated

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</blockquote>

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with that namespace. The same identifier can be independently defined in multiple

In programming languages that do not provide language support for namespaces, namespaces

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<p>In programming languages that do not provide language support for namespaces, namespaces can be emulated to some extent by using an identifier naming convention. For example, C libraries such as Libpng often use a fixed prefix for all functions and variables that are part of their exposed interface. Libpng exposes identifiers such as:</p>

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can be emulated to some extent by using an identifier naming convention. For example,

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C libraries such as Libpng often use a fixed prefix for all functions and variables that

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are part of their exposed interface. Libpng exposes identifiers such as:

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png_create_write_struct

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png_get_signature

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png_read_row

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png_set_invalid

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This gives reasonable assurance that the identifiers are unique and can therefore be used

In computer programming, a fully qualified name is an unambiguous name that specifies which object, function, or variable a call refers to absolutely. To fully-qualify most often means to explicitly refer to namespaces that would otherwise be implicit because of the scope of the call.

In computer programming, a fully qualified name is an unambiguous name that specifies which object, function, or variable a call refers to absolutely. To fully-qualify most often means to explicitly refer to namespaces that would otherwise be implicit because of the scope of the call.

In June of 2007, while discussing what should be the name of a song, album or audio recording for hAudio, [http://microformats.org/discuss/mail/microformats-new/2007-June/000511.html it was suggested that TITLE be re-used from hCard]. This kicked off a debate about whether it would be appropriate to re-use TITLE because [http://microformats.org/discuss/mail/microformats-new/2007-June/000512.html TITLE was previously defined in hCard as "job title"]. Manu pointed out that [http://microformats.org/discuss/mail/microformats-new/2007-June/000511.html this was not the proper English definition for TITLE], would confuse authors, and inquired as to why TITLE was defined in such a constrained way. It was shown that [http://microformats.org/discuss/mail/microformats-new/2007-June/000512.html TITLE re-used the definition of TITLE from the VCARD specification], and since TITLE had been set as such, re-defining it to become in-line with the English definition of TITLE would have ramifications on hCard implementations out in the field.

In June of 2007, while discussing what should be the name of a song, album or audio recording for hAudio, [http://microformats.org/discuss/mail/microformats-new/2007-June/000511.html it was suggested that TITLE be re-used from hCard]. This kicked off a debate about whether it would be appropriate to re-use TITLE because [http://microformats.org/discuss/mail/microformats-new/2007-June/000512.html TITLE was previously defined in hCard as "job title"]. Manu pointed out that [http://microformats.org/discuss/mail/microformats-new/2007-June/000511.html this was not the proper English definition for TITLE], would confuse authors, and inquired as to why TITLE was defined in such a constrained way. It was shown that [http://microformats.org/discuss/mail/microformats-new/2007-June/000512.html TITLE re-used the definition of TITLE from the VCARD specification], and since TITLE had been set as such, re-defining it to become in-line with the English definition of TITLE would have ramifications on hCard implementations out in the field.

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A suitable replacement for TITLE was discussed and, [http://microformats.org/discuss/mail/microformats-new/2007-October/001009.html FN was adopted for hAudio].

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A suitable replacement for TITLE was discussed and [http://microformats.org/discuss/mail/microformats-new/2007-October/001009.html FN was adopted for hAudio].

Several months later, Martin McEvoy [http://microformats.org/discuss/mail/microformats-new/2008-January/001375.html raised the issue again] - that FN is not a suitable replacement for the title of an audio recording. Manu [http://microformats.org/discuss/mail/microformats-new/2008-February/001401.html argued that TITLE should be brought in line with the English definition] once again, and another argument about namespacing started on the microformats-new mailing list. This discussion revolved around an assertion that Manu was making about Microformat's [http://microformats.org/wiki/namespaces having a stance against namespacing], but then turning around and [http://microformats.org/discuss/mail/microformats-new/2008-February/001401.html inconsistently using "emulated namespaces"] as a replacement when there was no other option but to namespace (such as in hAtom - "entry-title", "entry-summary", "entry-description")

Several months later, Martin McEvoy [http://microformats.org/discuss/mail/microformats-new/2008-January/001375.html raised the issue again] - that FN is not a suitable replacement for the title of an audio recording. Manu [http://microformats.org/discuss/mail/microformats-new/2008-February/001401.html argued that TITLE should be brought in line with the English definition] once again, and another argument about namespacing started on the microformats-new mailing list. This discussion revolved around an assertion that Manu was making about Microformat's [http://microformats.org/wiki/namespaces having a stance against namespacing], but then turning around and [http://microformats.org/discuss/mail/microformats-new/2008-February/001401.html inconsistently using "emulated namespaces"] as a replacement when there was no other option but to namespace (such as in hAtom - "entry-title", "entry-summary", "entry-description")

Revision as of 16:32, 5 February 2008

Contents

Introduction

This page outlines a disputed inconsistency that the Microformat's community has had for a number of years. Namely, in the way the community defines "namespace" and the position it takes against that definition of a namespace.

Brief Definitions

Here are the definitions that the namespace inconsistency deals with:

context</dt>

A context is an enclosing structure that provides semantic meaning to the elements that it encloses.

scope</dt>

A scope is an enclosing context where values and expressions are associated. The term is interchangeable with context.

namespace</dt>

A namespace is a named scope.

fully qualified namespace</dt>

Fully qualified namespaces remove all ambiguity from a name. An example of a fully qualified namespace is: http://purl.org/dc/elements/1.1/creator, which is a fully qualified namespace for the Dublin Core property named 'creator'. In C++ std::string is an example of a fully qualified namespace.

emulated namespace</dt>

A namespace can be emulated by using an identifer naming convention. For example, png_create_write_struct, png_get_signature, png_read_row, png_set_invalid are examples of C functions that use an emulated namespace called 'png'.

Required Changes

These are the changes that would need to be made to the namespaces page to bring the Microformats definition of a namespace in line with the commonly cited definition of a namespace.

The five brief definitions on context, scope, namespace, fully qualified namespace, and emulated namespace should be included on the page. Citations to more detailed definitions should be included on the page, the list of literature at the end of this page would be a good starting point.

It should be made clear that Microformats use context, scope, namespaces as a general concept, and emulated namespaces in certain situations.

It should be made clear that Microformats do not use fully qualified namespaces for class names, data, or any other Microformatted content.

Definitions

Here are excerpts from the definitions and links to further definitions supporting the arguments listed on this page.

The general definition of context is:

<p>Discourse that surrounds a language unit and helps to determine its interpretation.</p>

In computer programming, scope is an enclosing context where values and expressions are associated. Various programming languages have various types of scopes. The type of scope determines what kind of entities it can contain and how it affects them -- or semantics.

Scopes can:

contain declarations or definitions of identifiers;

contain statements and/or expressions which define an executable algorithm or part thereof;

nest or be nested.

A namespace is a scope that uses the enclosing nature of the scope to group logically related identifiers under a single identifier. Thus, scopes can affect the name resolution for their contents.

...a namespace is an abstract container providing context for the items (names, or technical terms, or words) it holds and allowing disambiguation of items having the same name (residing in different namespaces)...

A namespace is an abstract container or environment created to hold a logical grouping of unique identifiers (i.e., names). An identifier defined in a namespace is associated with that namespace. The same identifier can be independently defined in multiple namespaces. That is, the meaning associated with an identifier defined in one namespace may or may not have the same meaning as the same identifier defined in another namespace. Languages that support namespaces specify the rules that determine which namespace an identifier (i.e., not its definition) belongs.

In programming languages that do not provide language support for namespaces, namespaces can be emulated to some extent by using an identifier naming convention. For example, C libraries such as Libpng often use a fixed prefix for all functions and variables that are part of their exposed interface. Libpng exposes identifiers such as:

png_create_write_struct

png_get_signature

png_read_row

png_set_invalid

This gives reasonable assurance that the identifiers are unique and can therefore be used in larger programs without fear of identifier naming collisions.

In computer programming, a fully qualified name is an unambiguous name that specifies which object, function, or variable a call refers to absolutely. To fully-qualify most often means to explicitly refer to namespaces that would otherwise be implicit because of the scope of the call.

Manu asserted further that the community has an inconsistent stance on namespaces because the community's definition of namespacing was not standard. It deviated from the definition in the field of linguistics, programming language design, and mainstream computer science literature. To illustrate the point, it was shown what the standard definition of 'namespace' is using a number of text books on the subject.

Manu is currently challenging the vague and inconsistent definition of namespace that is being used in the Microformats community and is asking for further refinement on the types of namespaces that are and are not allowed in the Microformats community.

Sympathetic to the Cause

Below is a list of people that would like the namespace inconsistency more directly addressed by implementing the changes listed above in the "Required Changes" section.